The present invention relates generally to electric coils, and more particularly to a method and apparatus for coating an electric coil.
Workpieces, such as parts of electric motors including armatures, stators, and the like, have electric coils which are often coated with a resin to immobilize together coil windings with adjacent coil windings and immobilize together coil windings with adjacent non-coil structure of the workpiece. For example, when manufacturing armatures, a known coating technique is to trickle a resin onto the wire windings (i.e., the electric coil) of the armature as the armature rotates about its longitudinal axis. Once cured, the resin locks the wires together to reduce excessive vibration of the wire windings when the armature is operating in an electric motor. Without such a coating, or with an incomplete coating having void spaces, excessive vibration of the insulated wire of the wire windings of the electric coil typically leads to a break in the insulation and a shorting out of the electric motor. In order to prepare the workpieces for the application of resin to the electric coil, the workpieces typically are pre-heated to aid the flow of resin on the electric coil of the workpiece. Preheating the workpieces helps to xe2x80x9cwickxe2x80x9d the resin onto unexposed portions of the coil windings and into the spaces between coil windings and adjacent coil windings and between coil windings and adjacent non-coil structure of the workpieces through a capillary action. In order to more quickly cure the resin, the workpieces typically are post-heated after being coated with the resin.
Workpieces typically are preheated and post-heated by passing the workpieces under radiant heating elements. However, when using radiant heating elements, the distance between the workpieces and the radiant heating elements must be maintained at precise levels to avoid overheating or underheating of the workpieces. Furthermore, the sequence timing (i.e. the residence time of a workpiece underneath a radiant heating element) must be precisely controlled to avoid overheating or underheating of the workpieces. For example, if the conveyor that transports the workpieces must be temporarily shut down for maintenance, overexposure of the workpieces to the radiant heating elements may damage the workpieces.
U.S. Pat. No. 5,401,531 discloses that workpieces can be preheated and post-heated in ovens (before and after trickle coating their electric coils with a resin) by introducing high-temperature, undoubtedly-low-velocity (i.e., less than 50 feet per minute) air into the ovens from blowers and conventional heat exchangers. The blowers are aligned away from the workpieces which travel along a serpentine-shaped conveyor path toward, and away from, the blowers. All exterior surfaces of the workpieces are exposed to air of substantially the same temperature in an oven, and the workpieces require a significant period of time to absorb the ambient heat in an oven. These ovens also requires a relatively large amount of space.
Applicant is aware of an oven used to preheat workpieces (before trickle coating their electric coils with a resin), wherein high-temperature, low-velocity (believed to be less than 50 feet per minute) air enters the oven from a line of spaced-apart holes in a side of a manifold. The workpieces travel, in start-and-stop stages, along a serpentine path in the oven at a constant distance of between 5 and 8 inches from the side of the manifold having the holes. Each workpiece is stopped, in turn, during a same one of the start-and-stop stages, opposite a same one of the holes. It is not known if the workpieces stop opposite any of the other holes. The longitudinal axis of each workpiece is aligned parallel to the central axes of the holes. All exterior surfaces of the workpieces are exposed to air of substantially the same temperature in the oven, and the workpieces require a significant period of time to absorb the ambient heat in the oven. This oven also requires a relatively large amount of space.
Applicant also is aware of ovens in some restaurants which heat a piece of food by blowing high-temperature, high-velocity (i.e., greater than 500 feet per minute) air directly onto the piece of food.
What is needed is a faster method and apparatus for coating an electric coil of a workpiece.
A first method of the invention is for coating an electric coil of a workpiece and includes steps a) and b). Step a) includes directing a first heated gas flow to impinge on the workpiece, wherein the first heated gas flow first impinging the workpiece has a velocity of at least generally 500 feet per minute. Step b) includes applying a coating material to the electric coil of the workpiece. In a first example of the first method, step a) is performed before step b). In a second example of the first method, step a) is performed after step b). In a third example of the first method, step a) is performed before and after step b). Preferably, in an implementation of the first method, the first heated gas flow is a heated air flow. Preferably, in another implementation of the first method, in step a), the first heated gas flow first impinging the workpiece has a temperature between generally 200 degrees Fahrenheit and generally 400 degrees Fahrenheit. Preferably, in a further implementation of the first method, the coating material is a liquid including a resin, and step b) includes trickling the coating material onto the electric coil of the workpiece.
A second method of the invention is for coating an electric coil of a workpiece and includes steps a) and b). Step a) includes directing a first heated gas flow to impinge on the workpiece substantially perpendicular to the longitudinal axis of the workpiece. Step b) includes applying a coating material to the electric coil of the workpiece. In a first example of the second method, step a) is performed before step b). In a second example of the second method, step a) is performed after step b). In a third example of the second method, step a) is performed before and after step b). Preferably, in an implementation of the second method, there is also included, during step a), the step of rotating the workpiece about the longitudinal axis.
An embodiment of the invention is apparatus for coating an electric coil of a workpiece. The apparatus includes a first mechanism for directing a first heated gas flow to impinge on the workpiece, wherein the first heated gas flow first impinging the workpiece has a velocity of at least generally 500 feet per minute. The apparatus also includes a second mechanism for applying a coating material to the electric coil of the workpiece. The apparatus further includes a third mechanism for relatively transporting the workpiece between the first mechanism and the second mechanism. Preferably, the first heated gas flow first impinging the workpiece has a temperature between generally 200 degrees Fahrenheit and generally 400 degrees Fahrenheit. Preferably, the second mechanism includes a liquid-resin trickle dispenser.
Several benefits and advantages are derived from the invention. It is noted that heating with a heated gas flow will avoid the overheating and underheating problems encountered when heating with radiant heaters. In a workpiece heating operation, before and/or after applying a coating material to the electric coil of the workpiece, the high-temperature, high-velocity gas (such as air) flow impinging the workpiece heats the workpiece more quickly than conventional ovens which blow in high-temperature, low-velocity air to heat the oven chamber to heat the workpiece. This is analogous to heat-drying a person""s wet hair using a directed air flow from a hair blow-dryer held a couple of inches from the wet hair versus heat-drying a person""s wet hair by having the person stand in the middle of a room heated by forced hot air entering from a floor register along a wall of the room. Conventional ovens also require time to heat a cold oven. Directing the high-temperature, high-velocity gas (such as air) substantially perpendicular to the longitudinal axis of the workpiece impinges more surface area to more quickly heat the workpiece than do other orientations, and rotating the workpiece about the longitudinal axis allows a single gas (such as air) flow to more quickly heat the workpiece. Applicant has pre-heated workpieces for trickle coating in about seven minutes using his invention where conventional ovens would take about fifteen minutes.